Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicinal product, such as liquid drugs, and further providing administration of the liquid to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose.
In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
Typically, the medicinal product to be administered is provided in a cartridge that has a moveable piston or bung mechanically interacting with a piston rod of a drive mechanism of the drug delivery device. By applying thrust to the piston in distal direction, a certain amount of the medicinal fluid is expelled from the cartridge.
Drug delivery devices, such like pen-type injectors typically comprise a housing having a cartridge holder for receiving the cartridge filled with the medicinal product that has to be dispensed. The distal end section of a cartridge holder facing towards the patient during an injector procedure typically comprises a through opening that provides access to a sealed distal end of the cartridge. By way of said through opening, an injection needle or cannula may penetrate the elastic seal of the cartridge to establish a fluid interconnect allowing the medicinal product to be expelled from the cartridge.
Typically, the disposable injection needle is provided by way of a needle assembly for releasably fastening the injection needle to the cartridge holder. The needle assembly typically comprises a needle hub supporting the injection needle and having further a cupped receptacle with an inner thread to be screwed onto a correspondingly threaded distal socket of the cartridge holder. The needle hub is typically provided with a removable needle cap serving as a protection means for preventing inadvertent stitch damage.
For administering a dose of the medicament, the needle cap has to be removed, before the needle pierces the skin of the patient. Upon completion of the medicament injection procedure, the needle is removed from the biological tissue and prior to disassembling needle hub and cartridge holder, the protective needle cap should be mounted on the needle hub. Inadvertent stitch damages may particularly occur, when the patient mounts the needle cap back on the needle hub. This problem is getting even more severe when the patients are physically infirm and/or have impaired vision.
It is therefore an object of the present invention to provide an improved cap assembly for a drug delivery device that serves as a tool at least for disassembling a needle assembly from a cartridge holder of a drug delivery device. It is a further aim, to reduce the risk of stitch damages and to enhance patient safety. Moreover, the cap assembly should be easy in understanding by the patient of its use. The cap assembly should also be particularly cost efficient in terms of production costs and assembly expenditure.